This invention relates to a method of and an apparatus for using an image taken of a component mounting substrate (herein referred to simply as a substrate) to inspect the presence or absence of components, their positional displacements and appropriateness of soldering.
As disclosed in Japanese Patent Publication 2003-222598, the present assignee of this invention has developed a substrate inspection apparatus for automatically inspecting mounted conditions and soldering conditions of components. This inspection apparatus is provided with a substrate stage for supporting a target substrate which is the object of inspection, a camera for taking an image of the substrate and a table part (including both an X-axis part and a Y-axis part) for moving the substrate stage and the camera on a horizontal plane. At the time of an inspection, each table part is controlled so as to match the field of vision of the camera with a specified area on the substrate. An image obtained under this condition is processed in order to make measurements that are necessary for the inspection of target portions to be inspected inside this specified area and measured values thus obtained are compared with specified standard values.
With an inspection apparatus of this kind, a process referred to as the teaching process is usually carried out prior to the inspection wherein inspection data of various kinds are prepared and registered in a memory. The so-called setting data of inspection areas that are set at each target inspection portion are included in the inspection data. At the time of an inspection, inspection areas are set on the image of the target substrate to be inspected (hereinafter referred to as the target image) based on the aforementioned setting data and the inspection of each target inspection portion is carried out by processing the image of each inspection area.
In order to carry out an inspection process as described above, it is necessary to adjust the position of the substrate or the camera such that the target inspection portion on the substrate will be placed according to the setting data of the inspection area. According to a general prior art method, positioning marks are attached to appropriate positions on the substrate, these marks are extracted from the image of the substrate after it is transported into the image-taking position, and the X-axis and the Y-axis parts are controlled such that these extracted positions will match preliminarily specified reference positions.
Japanese Patent Publication Tokkai 9-15302 discloses a technology similar to the one described above, according to which two positioning patterns are extracted from an image of the substrate, the position of the substrate stage is adjusted such that the middle point of the line segment connecting these two extracted positions will match the middle point of the line segment connecting reference positions of these patterns and the substrate stage is further rotated by the angle between these two line segments.
By such a method of controlling the driving mechanism for the substrate stage, however, it is not possible to overcome the effects of errors due to the characteristics of the driving mechanism. Since very small components are coming to be mounted to substrates and at a very high density in recent years, the error in the positioning of the substrate may be small but an error may be generated in the setting of inspection area and incorrect inspection results may be obtained. In order to reduce the error, a highly accurate driving mechanism will be required and this affects the cost adversely.